1. Field of the Invention
The present invention relates to a planographic printing plate, and in particular, to a planographic printing plate in which an aluminum plate is employed as a support element. In addition, the present invention pertains to a non-woven cloth roller and a method and apparatus for preliminarily polishing a metal plate for printing plate. In particular, the present invention relates to a non-woven cloth roller for preliminarily polishing a running web-shaped metal plate for printing plate and a preliminary polishing method and apparatus using the roller.
2. Description of Related Art
In general, in order to use an aluminum plate as a support element of a planographic printing plate, it is required to have appropriate adhesive properties to a photosensitive material and water preserving properties, and further, make the plate uniformly surface-roughened. Being uniformly surface-roughened means that the sizes of produced pits are appropriately equal, and requires that such pits are uniformly produced on their full faces. In addition, the pits considerably influence dirt retardant properties, printing resistance or the like that are printing performances of a printing plate material, and its quantity is an important factor for making a printing plate. Further, in recent years, a computer system for direct plate making from digital signals or the like is becoming popular with advancement of information system. In particular, with advancement of miniaturization and high yielding of solid laser and semiconductor laser beams, such computer system is becoming rapidly popular. It is also anticipated that a planographic printing plate support element restricts laser beam halation, and provides water preserving properties, hydrophilicity, printing resistance, and dirt retardant properties which are important for a printing plate.
As a recording material for infrared-ray laser beams, in Japanese Patent Publication No. 61-48418, there is disclosed an anodic oxidation support element having at least an oxide layer of 5 to 12 g/m2. In addition, in Japanese Patent Laid-Open No. 63-260491, there is proposed a surface-roughened and anode-oxidized support element in which a sol having a nuclei to be reduced to a silver complex is adhered. In U.S. Pat. No. 4,555,475, there is proposed a support element silicate-treated on a surface having an anodic oxidation skin film to form a silicate of aluminum of 2 to 8 mg/m2. In EP 164128B also, there is proposed a method for graining an aluminum surface, anodic oxidation, causing silicate treatment, applying a carbon black to make a photosensitive material, thereby forming an image. Further, in Japanese Patent Laid-Open No. 10-228992, there is proposed a support element for restricting halation.
However, although the above patents are superior inventions, there has been requested further improvement of productivity and stability of small dot net portions due to improvement of adhesion.
In a web-shaped metal plate for printing plate, for example, a thin aluminum plate or aluminum alloy plate, its surface is polished, fine irregularities called grains are formed and surface-roughened, thereby improving printing adaptability of a metal plate for printing plate.
At present, a polishing method generally performed for surface-roughening of the metal plate for printing plate includes mechanical polishing employing a roller brush (for example, Japanese Patent Publication No. 50-40047); electrochemical polishing for performing electrolysis in an electrolyte; or chemical polishing for immersing in chemicals.
In the case where mechanical polishing, electrochemical polishing, or chemical polishing is carried out for a metal plate for printing plate such as aluminum plate having recesses locally, there is an abnormality that uniform surface-roughening is impossible at such recesses, thus lowering the printing performance at such portion.
As a countermeasure for eliminating such abnormality, the Applicant adopts that prior to polishing, the surface of the running metal plate for printing plate is preliminarily polished by a non-woven cloth roller containing polishing agent.
However, where the metal plate for printing plate is preliminarily polished by a conventional non-woven cloth roller, although a graining failure can be prevented while in polishing, there is a disadvantage that an appearance failure (polishing streak) which seems to be caused by the polishing agent occurs on the surface of the metal plate for printing plate while in preliminary polishing.
Further, in a conventional preliminary polishing method, there is a disadvantage that non-uniformity of preliminary polishing occurs on the surface of the metal plate for printing plate to be preliminarily polished, impurities such as Cu or Fe segregated at the top layer portion of the metal plate for printing plate remain, and a graining failure occurs in the subsequent polishing.
The present invention has been achieved in view of the foregoing circumstance. It is an object of the present invention to provide a planographic printing plate capable of ensuring improvement of productivity and stability of small dot net portions due to improvement of adhesion.
To achieve the foregoing object, the present invention provides a planographic printing plate wherein a surface of an aluminum plate, a support element, of a planographic printing plate has been subjected to preliminary polishing mechanically by at least 0.1 xcexcm; chemical etching treatment by at least 0.1 xcexcm ; electrochemical surface-roughening; and anodic oxidation, and a surface structure of the aluminum plate is characterized in that: (a) an area (S) for a graphic formed by a reference straight line drawn from a top of a third highest mountain of a two-dimensional roughness curve downwardly by 1 xcexcm and a roughness curve above the reference straight line is 30 xcexcm2xe2x89xa6Sxe2x89xa6150 xcexcm2; (b) an average roughness Ra of average lines is 0.15 xcexcmxe2x89xa6Raxe2x89xa60.60 xcexcm; (c) a relationship between the average roughness Ra of average lines and a height Rp of a center line is Rpxe2x89xa66Ra; (d) a relationship between a maximum height Rmax and the average roughness Ra of average lines is Rmaxxe2x89xa612Ra; and (e) a surface area difference is between 20% and 70%.
It is another object of the present invention to provide a method and apparatus for preliminarily polishing a non-woven cloth roller and a metal plate for printing plate free of polishing streaks on the surface of the metal plate for printing plate in preliminary polishing, the metal plate being capable of preventing a graining failure while in polishing.
To achieve the foregoing object, the present invention provides the non-woven cloth roller having a polishing agent contained in a roll-shaped non-woven cloth, characterized in that an average particle size of the polishing agent contained in the non-woven cloth is at most 50 xcexcm, a maximum particle size is at most 60 xcexcm, and density of the polishing agent on a fiber surface of the non-woven cloth is at least 60%.
To achieve the foregoing object, the present invention provides a method for preliminarily polishing a metal plate for printing plate, wherein a surface of the running web-shaped metal plate for printing plate is preliminarily polished by a non-woven cloth roller containing the polishing agent as preprocessing for polishing and surface-roughening of the metal plate for printing plate, the method characterized in that: an average particle size of the polishing agent contained in the non-woven cloth prior to starting use of the non-woven cloth roller is at least 50 xcexcm, the maximum particle size is at most 60 xcexcm, and the density of the polishing agent on the fiber surface of the non-woven cloth is at least 60%.
To achieve the foregoing object, the present invention provides an apparatus for preliminarily polishing a metal plate for printing plate, wherein the surface of a running web-shaped metal plate for printing plate is preliminarily polished as preprocessing for polishing and surface-roughening of the metal plate for printing plate, the apparatus characterized by comprising: a non-woven cloth roller disposed at one side having the metal plate for printing plate sandwiched, wherein the average particle size of the polishing agent contained in a roll-shaped non-woven cloth is at most 50 xcexcm, the maximum particle size is at most 60 xcexcm, and the density of the polishing agent on the fiber surface of the non-woven cloth is at least 60%; support rollers disposed in one pair on the other side having the metal plate for printing plate sandwiched with predetermined intervals, the support rollers supporting the metal plate for printing plate; a forwarding and retracting device for pressing the non-woven cloth roller to the support roller side and pushing the metal plate for printing plate between the pair of support rollers; and a water supply device for supplying water to a surface of the metal plate for printing plate.
According to the present invention, there is used a non-woven cloth roller, wherein the average particle size of polishing agent contained in a roll-shaped non-woven cloth is at most 50 xcexcm, the maximum particle size is at most 60 xcexcm, and the density of the polishing agent on the fiber surface of the non-woven cloth is at least 60% so as to preliminarily polish the metal plate for printing plate. Thus, in preliminary polishing, no polishing streak occurs on the surface of the metal plate for printing plate, and a graining failure can be prevented while in polishing.
Further, to achieve the foregoing object, the present invention provides a method for preliminarily polishing a metal plate for printing plate, wherein a surface of the running web-shaped metal plate for printing plate is preliminarily polished by a non-woven cloth roller containing a polishing agent as preprocessing for polishing and surface-roughening the metal plate for printing plate, the method characterized in that when a peripheral rotation speed of the non-woven cloth roller is defined as V1 (m/minute), a running speed of the metal plate for printing plate is defined as V2 (m/minute), the average particle size when the polishing agent contained in the non-woven cloth roller is represented by a diameter corresponding to a circle is D (xcexcm), and the preliminary polishing quantity of the metal plate for printing plate is defined as X (xcexcm), the V1, V2, D, and X is set so as to meet the following formula to make preliminary polishing: 5xe2x89xa6Dxc3x97V1xc3x97X/V2xe2x89xa620000.
According to the present invention, the peripheral rotation speed of the non-woven cloth roller is defined as V1 (m/minute); the running speed of the metal plate for printing plate is defined as V2 (m/minute); the average particle size when the polishing agent contained in the non-woven cloth roller is represented by a diameter corresponding to a circle is defined as D (xcexcm); and the preliminary polishing quantity of the metal plate for printing plate is defined as X (xcexcm), thereby causing preliminary polishing so as to meet 5xe2x89xa6Dxc3x97V1xc3x97X/V2xe2x89xa620000. Thus, the non-uniformity of preliminary polishing does not occur, and a graining failure can be prevented while in polishing.